The present invention relates to an anchor (or connector) which can be used to fasten organic tissue in close proximity in order to afford the tissue the opportunity to heal. The anchor of the present invention can be used to anchor and clamp dense, regular and/or dense, irregular connective tissue in place in relation to bone. The anchor can also be used for tissue transplants, i.e., for holding tissue in fixed relation to bone, and can also be used in bone as a buttress, such as for buttress plating techniques, or to fasten pieces of bone together as a screw substitute. Further, the anchor can be used in soft tissue applications. Thus, as used herein “tissue anchor” relates broadly to the invention used as a screw, clamp, or anchor in the narrow sense of the word which holds organic tissue, i.e. bone to bone, soft tissue to bone, or soft tissue to soft tissue.
As compared to the prior art, the anchor of the present invention allows a method of holding together organic tissue with minimal disruption to the biological environment or to the tissue itself. For example, prior art devices and methods customarily require a large hole for insertion of the anchoring device, causing not only structural damage to the implantation site, but also inflicting further trauma to the biological site such as generating heat, introducing further possibility for infection, and destroying bone which may be needed to help heal the repaired area. Such trauma is amplified in cases where prior art devices malfunction during the implant procedure. Hooks or screws can get stuck and further obscure the operating site or require tedious removal.
The anchor of the present invention may be very useful for applications such as anchoring ligaments or tendons when performing soft tissue surgical reconstruction, rupture tendons, or torn ligaments, in which the surgeon wants to reconstruct or repair connective tissue with respect to the bone or with respect to other soft tissue.
The anchor device functions to hold together the tissue (such as connective tissue to bone) for a relatively limited time frame e.g., six to twenty-six weeks, during which time the biological system will heal.
The anchor of the present invention can be used with advantage in many of the same applications in which cancellous screws are used in addition to applications in which traditional prior art anchoring techniques are unsatisfactory. The anchor of the present invention is far less invasive to implant than cancellous screws or hook-style anchors, i.e., the implant has a minimized mass, the insertion point is small relative to the size of the implant, and the device involves minimal removal of native tissue. In addition, the area of bone or other tissue which is needed to secure the present invention can be of poorer quality than for prior art devices.
Additionally, the anchor of the present invention can be removed and minimally reangulated in order to utilize the same surgical site. Prior art devices require a large hole (relative to implant size) to be drilled in order to implant the device, and once the hole is contaminated by malfunction or misalignment of the device, it is necessary to drill another hole far enough away to achieve stability in a new location. Given the surgical context, this is extremely inconvenient.
The anchor of the present invention can be used in methods of ligament, tendon, or other tissue repair. For example, the anchor can be used for a method involving cartilage transplant and it can be used alone or in conjunction with a plate for a method of buttressing bone where the quality of bone may be questionable due to trauma or degenerative disease. The anchor may be used in methods of fixation involving connective tissue repair and replacement and may be inserted using a plunge-handle or “T” handle inserter which utilizes longitudinal travel in order to achieve rotational insertion. The handle and insertion tool may be a standard screwdriver or a jig-outer cannula system for a hex head or headless helix, respectively.
Specifically, the anchor is used in a ligament or tendon in which a pilot hole, having a diameter much smaller than the outer diameter of the helical anchor, is drilled in the cortex of the bone. The angle of implantation can be varied as necessary. The anchor is subsequently mounted or loaded into the insertion tool, threaded into the pilot hole, and screwed into the bone an appropriate distance so that the anchor head can be accessed but is not obtrusive. The ligament or tendon is attached to the anchor, such as by suturing.
In addition, the anchor of the present invention can be used to anchor plates and is particularly useful in instances where the bone is of poor quality. The head can be a bend in the wire which forms a cross bar and which can be implanted using a slotted instrument. A particularly desirable head for some applications has an internal hex slot to permit the anchor to be implanted. In addition, the head has a transverse through slot to hold a suture. The head has a low, rounded profile with a distal stem which fits inside a ring of the helix and is laser-welded thereto. In an alternative embodiment, the anchor has a solid cylindrical head which extends from the spiral and has the same outer diameter. This head also has an internal torque receiving hexagon, which has a hole in the center of the bottom surface of the hex shaped recess. This hole allows for cannulation for implantation. Further, the head has a hole (or more precisely, two aligned holes), in a direction transverse to the longitudinal axis of the spiral to allow a suture to be attached to the head. For the screw used with a plate, the screw may have a head with a diameter that exceeds the diameter of the helix, or a conical washer may be used which allows for angulation of the head in the plate, or the head may include external threads that mate with internal threads in the plate. In an alternative embodiment, the head comprises a rivet or clamp, which can be fixed to a boss formed at the top of the helical structure. This version of the anchor can be driven into bone using matching Male-Female head.
Moreover, in accordance with an aspect of the invention, the structure is made by forming a screw type blank having an externally threaded member which extends from a cylindrical head having an internal torque receiving recess, preferably a hexagon. The blank is subsequently drilled internally to form an open helical structure attached to the solid head. The material removed is tapered along the long axis decreasing in the direction of the top of the helical structure where the apex of the cone is at the proximal position of the helix. This places more material at the driver level where the helix joins the head and takes the driving torque. The conical opening may still include a through hole for cannulation. In addition, it has been found to be an advantage for the helix to include a taper from the insertion end toward the head in the direction of the longitudinal length of the filament. This provides for significantly higher test results in the pull-out strength.